The present invention is directed to a speakerphone for use with a telephone system and more specifically with a speakerphone which has a dynamic level discriminator in the microphone channel.
In a typical speakerphone system in order to prevent feedback between the microphone and loudspeaker it is necessary to provide a switching circuit to alternately control the microphone channel and the speaker channel. This is usually done by appropriate rectifiers which sense the audio signal level of either channel and connect the channel with the maximum audio signal to the telephone line or communications link.
In addition such circuits, in order to distinguish the noise from an audio signal in the microphone channel, may include a fixed threshold level in the microphone channel above which the speech level must be in order to be effectively transmitted. Such a system is inadequate where either the ambient noise is quite high, which might cut out the speaker channel completely, or where the audio signal itself varies widely in its peak levels. In other words, there is a basic problem between distinguishing audio signal amplitude which is desired to be transmitted with ambient noise signals.